Thixotropic anhydrous shear thinning peroxide dispersions

ABSTRACT

Provided are dispersions which comprise more than about up to 55 percent by weight or more of an organic peroxide which is normally solid in an anhydrous liquid phase such as dibutyl maleate or dioctyl adipate, with about 5% by weight or more fumed silica to provide a thixotropic, storage stable organic peroxide paste. Addition of about 5 weight % or more of fumed silica was found to result in the formation of a shear thinning anhydrous dispersion of organic peroxide which was storage stable.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/147,457, filed Aug. 2, 2011, which is a national stage applicationunder 35 U.S.C. § 371 of PCT/US2010/022959, filed Feb. 3, 2010, whichclaims benefit to U.S. Provisional Application No. 61/149,445, filed onFeb. 3, 2009, all of which are hereby incorporated by reference.

FIELD OF INVENTION

The present invention relates to anhydrous pastes of organic peroxides.The pastes are phthalate free and exhibit thixotropic properties. Thatis, the pastes are shear thinning so as to be pumpable/pourable whenmixed or stirred which makes their handling and use easier.

BACKGROUND

Peroxides have, as a general property, a tendency to be flammable andexplosive with some peroxides exhibiting such properties to a greaterextent than others. For example, benzoyl peroxide may decompose when drydue to shock, friction, or static electricity. This property carrieswith it the obvious hazards to the users of these materials as well asto the manufacturers and intermediate handlers thereof. One particularlyburdensome aspect of this property occurs during shipment of theperoxides. Accordingly, it has long been an object to provide flameresistant organic peroxide compositions. For example, U.S. Pat. No.3,507,800 is directed to providing a flame resistant peroxidecomposition consisting essentially of three components—water, peroxideand solvent wherein the water is at least about 18 percent of thecomposition.

The safety and end-use advantage provided by water-soluble orwater-emulsifiable peroxides is recognized. U.S. Pat. No. 3,825,509describes a process for the suspension polymerization of vinyl chloridewherein the initiator is an aqueous emulsion of an organic peroxide inwhich the peroxide is present in an amount up to 19 weight percent. Thesurfactant used to prepare the aqueous peroxide emulsion is acombination of polyvinyl alcohol and polyoxyethylene sorbitanmonolaurate. However, emulsions containing greater than about 19 percentby weight of organic peroxide are described as being too viscous andtherefore difficult to handle.

There have been attempts in the past to make peroxide dispersions. U.S.Pat. Nos. 4,039,475 and 4,092,470 disclose stable, pumpable aqueoussuspensions of organic peroxides using a mixture of a) nonionicemulsifiers having a maximum HLB value of 12.5 and b) nonionicemulsifiers having a minimum HLB value of 12.5 or anionic emulsifiers.U.S. Pat. No. 4,734,135 discloses aqueous suspensions of solid organicperoxides using a protective colloid, a surface active agent and water.U.S. Pat. No. 4,440,885 teaches emulsions of a solid organic peroxideusing an emulsifier having an HLB value from about 9 to about 20, ahydrocarbon solvent and water.

Organic peroxides are used as initiators in polymerization operationssuch as for acrylic and polyester polymerizations. The organic peroxidessuch as benzoyl peroxide are commercially available assolutions/dispersions in phthalates such as dimethyl phthalate anddibutyl phthalate. Due to a perception of toxicity issues withphthalates, there is a current effort to discontinue their use in theproduction of polymers for certain uses.

SUMMARY OF THE INVENTION

The present invention is direct toward an anhydrous, phthalate free,peroxide paste which exhibits thixotropic properties. The anhydrous,phthalate free, peroxide paste of the present invention allows for thetransportation and handling of a peroxide paste having a highconcentration of peroxide which paste is shear thinning so it can beeasily pumped/poured and is also is resistant to separation uponstanding. The anhydrous, phthalate free, peroxide paste of the presentinvention is a paste of organic peroxide and fumed silica in a liquidphase. The liquid phase could be based upon diesters made from diacidssuch as C2-C10, saturated or unsaturated, and alcohols ranging from C1to C10. It was discovered that the addition of anhydrous fumed silica toan anhydrous benzoyl peroxide in dibutyl maleate or dioctyl adipatepastes resulted in an anhydrous paste which was shear thinning, i.e.thixotropic.

DESCRIPTION OF PREFERRED EMBODIMENTS

The anhydrous pastes of the present invention comprises an organicperoxide, which is normally solid, in a phthalate free, liquid phasesuch as dibutyl maleate or dioctyl adipate the mixture also includesanhydrous fumed silica. By phthalate free, within the scope of thepresent invention, is meant substantially free of phthalates and thatphthalates are not intentional add to the paste. It is intended thatphthalate free herein include pastes which contain trace amounts ofphthalates.

Exemplary of suitable organic peroxides are aromatic diacyl peroxides,such as benzoyl peroxide, o-methylbenzoyl peroxide, o-methoxybenzoylperoxide, o-ethoxy benzoyl peroxide, o-chlorobenzoyl peroxide and2,4-dichlorobenzoyl peroxide; aliphatic diacyl peroxides, such asdecanoyl peroxide, lauroyl peroxide and myristoyl peroxide; ketoneperoxides, such as 1-hydroxy cyclohexyl peroxide and1-hydroperoxycyclohexyl peroxide; aldehyde peroxides such as 1-hydroxyheptyl peroxide; peroxy dicarbonates such as dicetyl peroxydicarbonate,di(4-t-butylcyclohexyl) peroxydicarbonate and acylperoxyalkylcarbonates, such as acetyl peroxy stearyl carbonate and the like.

The pastes of the present invention comprise about 40 percent or more byweight of organic peroxide. One of the features of the present inventionis that it enables the preparation of pastes containing about 40 or morepercent by weight of organic peroxide which pastes are pumpable becausethey are shear thinning. Heretofore it has been difficult to makepumpable pastes containing about 40 or more percent by weight organicperoxide. In this description, shear thinning means that viscosity dropsas the shear rate increases. Thus, the viscosity of the peroxide pastesof the present invention will drop as the paste is stirred or mixed andit becomes pourable or pumpable easing use.

The organic peroxide is formed into a paste in a liquid phase such as asolvent/plasticizer such as dibutyl maleate or dimethyl maleate.Preferably the paste comprises about 40% and more preferably, 55% byweigh benzoyl peroxide in dibutyl maleate or dioctyl adipate. Theorganic peroxide paste is mixed with fumed silica in amounts greaterthan about 5% by weight to provide a thixotropic paste. It was foundthat when less than 5% of fumed silica was added to a 55 wt % benzoylperoxide in dibutyl maleate or dioctyl adipate paste, phase separationoccurred after a few days. However, when about 5% by weight of fumedsilica was added, an extremely viscous paste form which did not separateover time and exhibited thixotropic properties.

The anhydrous, phthalate free peroxide paste of the present invention isformed by simple mixing of the organic peroxide with the liquid phasefollowed by addition of the fumed silica. The fumed silica is a verylight fluffy power which is preferably added in multiple steps,typically three steps, in order to facilitate dispersion of the fumedsilica throughout the organic peroxide paste. Upon addition of the fullamount of fumed silica to the organic peroxide paste, the paste ispoured into a suitable shipping container where it will thicken. Thethickened paste can be easily removed from the container for use bymixing or stirring whereupon it becomes pourable.

The advantageous properties of this invention can be observed byreference to the following examples, which illustrate but do not limitthe invention.

EXAMPLES Example 1

A sample of paste in accordance with the present invention was preparedby combining anhydrous benzoyl peroxide and dibutyl maleate in a highshear mixer. After the peroxide was thoroughly dispersed, fumed silica(AEROSIL® 972 available from Evonik) was slowly added (typically inthree portions). The final paste was then mixed in a high shear blenderfor 30 to 60 seconds. The sample was the placed in a 25° C. ovenovernight. The following morning, the sample was removed from the ovenand stirred vigorously. The viscosity was measured over the followingthree hours.

Paste Composition:

Dibutyl Maleate 45% by weight Benzoyl Peroxide 50% by weight AEROSIL ®972  5% by weightApparatus: Brookfield Model DV-II+ ViscometerSpindle: T-C @2 rpm (helipath used)Temperature: 25° C.Viscosity:

Time Viscosity (Minutes) (cP) 0 4,500 5 55,000 10 81,500 30 124,500 60156,000 120 212,000 180 227,000

Example 2

A sample of paste in accordance with the present invention was preparedby combining anhydrous benzoyl peroxide and dioctyl adipate in a highshear mixer. After the peroxide was thoroughly dispersed, fumed silica(AEROSIL® 972 available from Evonik) was slowly added (typically inthree portions). The final paste was then mixed in a high shear blenderfor 30-60 seconds. The viscosity was measured over a two-hour period at22.5° C. (Room Temperature).

Paste Composition:

Dioctyl Adipate 45% by weight Benzoyl Peroxide 50% by weight AEROSIL ®972  5% by weightApparatus: Brookfield Model DV-II+ ViscometerSpindle: T-C@2 rpm (helipath used)Temperature: 22.5° C.Experimental Results:

Time Viscosity Minutes (cP) 0 2,500 5 20,000 10 31,000 30 44,500 6056,000 120 67,000

The data in examples 1 and 2 shows that the viscosity of the mixtureincreased significantly with time after the string is stopped, i.e. themixture was thixotropic. No phase separation was observed over time ineither example.

Having described the invention, we now claim the following and theirequivalents.

What is claimed is:
 1. An anhydrous shear thinning dispersion which isphthalate free and thixotropic, comprising about 40% by weight or moreof organic peroxide in an anhydrous liquid phase and about 5% by weightor more of anhydrous fumed silica based on total weight of thedispersion, wherein said anhydrous liquid phase comprises about 40% ormore of diesters derived from saturated and/or unsaturated C2-C10diacids.
 2. The anhydrous dispersion of claim 1, wherein said organicperoxide is selected from the group consisting of diacyl peroxides,aliphatic diacyl peroxides, ketone peroxides, aldehyde peroxides, peroxydicarbonates, acylperoxy alkylcarbonates and mixtures thereof.
 3. Theanhydrous dispersion of claim 2, wherein said diacyl peroxides areselected from the group consisting of benzoyl peroxide, o-methylbenzoylperoxide, o-methoxybenzoyl peroxide, o-ethoxy benzoyl peroxide,o-chlorobenzoyl peroxide, 2,4-dichlorobenzoyl peroxide and mixturesthereof.
 4. The anhydrous dispersion of claim 2, wherein said aliphaticdiacyl peroxides are selected from the group consisting of decanoylperoxide, lauroyl peroxide, myristoyl peroxide and mixtures thereof. 5.The anhydrous dispersion of claim 2, wherein said ketone peroxides areselected from the group consisting of 1-hydroxy cyclohexyl peroxide,1-hydroperoxycyclohexyl peroxide and mixtures thereof.
 6. The anhydrousdispersion of claim 2, wherein said aldehyde peroxides is 1-hydroxyheptyl peroxide.
 7. The anhydrous dispersion of claim 2, wherein saidperoxy dicarbonates are selected from the group consisting of dicetylperoxydicarbonate, di(4-t-butylcyclohexyl) peroxydicarbonate andmixtures thereof.
 8. The anhydrous dispersion of claim 2, wherein saidacylperoxy alkylcarbonate is acetyl peroxy stearyl carbonate.
 9. Theanhydrous dispersion of claim of claim 1, wherein said diesters madefrom diacids are selected from the group consisting of dimethyl maleate,dibutyl maleate and dioctyl adipate.
 10. The anhydrous dispersion ofclaim 1, wherein said anhydrous dispersion comprises about 55% by weightor more of said organic peroxide.
 11. A process of imparting thixotropicproperties to a phthalate free, thixotropic, anhydrous organic peroxidepaste resistant to separation upon standing and comprising 40% by weightor more of organic peroxide, said process comprising mixing, with saidpaste 5% by weight or more of anhydrous fumed silica, wherein saidanhydrous paste comprises a liquid phase comprising about 40% or morediester derived from saturated and/or unsaturated C2 to C10 diacids. 12.The process of claim 11, wherein said organic peroxide is selected fromthe group consisting of diacyl peroxides, aliphatic diacyl peroxides,ketone peroxides, aldehyde peroxides, peroxy dicarbonates, acylperoxyalkylcarbonates and mixtures thereof.
 13. The process of claim 12,wherein said diacyl peroxides are selected from the group consisting ofbenzoyl peroxide, o-methylbenzoyl peroxide, o-methoxybenzoyl peroxide,o-ethoxy benzoyl peroxide, o-chlorobenzoyl peroxide, 2,4-dichlorobenzoylperoxide and mixtures thereof.
 14. The process of claim 12, wherein saidaliphatic diacyl peroxides are selected from the group consisting ofdecanoyl peroxide, lauroyl peroxide, myristoyl peroxide and mixturesthereof.
 15. The process of claim 12, wherein said ketone peroxides areselected from the group consisting of 1-hydroxy cyclohexyl peroxide,1-hydroperoxycyclohexyl peroxide and mixtures thereof.
 16. The processof claim 12, wherein said aldehyde peroxides is 1-hydroxy heptylperoxide.
 17. The process of claim 12, wherein said peroxy dicarbonatesare selected from the group consisting of dicetyl peroxydicarbonate,di(4-t-butylcyclohexyl) peroxydicarbonate and mixtures thereof.
 18. Theprocess of claim 12, wherein said acylperoxy alkylearbonate is acetylperoxy stearyl carbonate.
 19. The process of claim 11, wherein saiddiester derived from diacids are selected from the group consisting ofdimethyl maleate, dibutyl maleate and dioctyl adipate.
 20. The processof claim 11, wherein said anhydrous dispersion comprises about 55% byweight or more of said organic peroxide.